Merge pull request #14488 from RudyLu/keyboard/Bug888253-keyboard_settings_migration

 Bug 888253 - Settings data migration for keyboard layouts.
r=gnarf, gary, yuren(cherry picked from commit 51ed5c6b6bda46284e797648b4b44dc9f804b14b)
a=koi+

Conflicts:
	build/settings.js